The Swiftest Planet Sun-scorched Mercury is only slightly larger than Earth's moon. Like the moon, Mercury has very little atmosphere to stop impacts, and it is covered with craters. Mercury's dayside is super-heated by the sun, but at night temperatures drop hundreds of degrees below freezing. Ice may even exist in craters. Mercury's egg-shaped orbit takes it around the sun every 88 days.

Light that is so blue humans cannot see it. A band of the spectrum between the ultraviolet and the gamma-ray. Photons of X-ray light are more energetic than photons in the ultraviolet but less energetic than photons in the gamma-ray. X-radiation can go through human skin tissue but is stopped by dense bones. This property thus makes X-rays valuable in medicine. It is also useful in observing outer space. Scientists used X-rays to discover strange auroral disturbances at Jupiter's north and south poles. (See image on right)

Light that is so blue humans cannot see it. A band of the spectrum between the ultraviolet and the gamma-ray. Photons of X-ray light are more energetic than photons in the ultraviolet but less energetic than photons in the gamma-ray. X-radiation can go through human skin tissue but is stopped by dense bones. This property thus makes X-rays valuable in medicine. It is also useful in observing outer space. Scientists used X-rays to discover strange auroral disturbances at Jupiter's north and south poles. (See image on right)